1. Field of the Invention
This invention relates generally to sheet delivering and more particularly to endless conveyor transport and stacking methods and apparatus.
2. Description of the Prior Art
A corrugated blank production machine or corrugator produces, in the first instance, an endless strip or web of corrugated board. Such corrugators cut endless strips of corrugated board by way of circular blades. This results in endless strips of corrugated board, running side by side, without any space between them. The cutting device of the corrugator usually has one circular cut-off knife whereby such endless strips of corrugated board are cut width-wise to various selected lengths. As a rule, this arrangement consists of at least one separate cut-off unit. Whenever there is more than one cut-off unit attached to the corrugator machine, then one of the units is placed higher than the other. A part of the former endless, but lengthwise cut corrugated strip, is brought to the upper knife while the other half is brought to the lower knife. Both knives can cut independently of each other to an adjustable length.
The result, therefore, is that a corrugator produces a stream of endless sheets or blanks. The sheets can be discharged as a single flow of sheets from the lower knife and a single flow from the upper knife or as a single flow from the upper or lower knives.
The continuous flow of sheets of board which are produced by the corrugator have to be received. For this purpose there are existing semi-automatic and fully automatic stacking machines. With the semi-automatic machines, stacks of blanks about 100 mm in height are formed, and these are carried off sideways (or indirectly) and further stacks are formed by way of manual labor. The fully automatic machine forms stacks of about 1800 mm high directly from the lower as well as the upper knife.
The biggest drawback of existing fully automatic machines is that the stacks of blanks are not precisely formed. That is to say, each blank is not stacked precisely above the blank below. Difficulty arises especially when the stacks are placed side by side. That is, the stacks catch or grip into each other, making it difficult to separate them. The forming of a new stack directly after a previously formed stack causes the most difficulty.
The corrugator machine continuously produces a stream of blanks and the receiving machine has to take care of temporary storage while stacks of the blanks are removed. Temporary storage is now taken care of by a machine which has a gate extending the full width of the machine. By closing the gate, the on-coming blanks are held up temporarily. During this temporary holdup, the blanks do not stay precisely aligned but extend randomly from side to side. When the previously formed stack is carried off, the gate opens and the blanks held in temporary storage become the lower half of the new stack. If the temporary stack being held up in front of the closed gate is imprecisely formed, then the new stack becomes worse in arrangement when it is advanced to the stacking place.
The foregoing has briefly described a single example of conventional stacking machines and problems associated therewith. Further examples may be had by reference to the following U.S. Pat. Nos.: 3,772,971; 2,274,075; 3,542,362; 3,683,758; 3,727,780; 3,550,493; 2,947,428; 3,297,174; and 3,373,666 which illustrate various approaches to the problem of stacking continuously flowing streams of articles, Although not necessarily corrugated paperboard blanks, and which are believed to reasonably represent the current state of the art.
Accordingly, an object of the present invention is to improve the methods and apparatus used for stacking continuously advancing streams of paperboard blanks and particularly to improve the quality of the stacks of blanks formed by such apparatus.